Age‐related decline in osteoblastogenesis and 1α‐hydroxylase/CYP27B1 in human mesenchymal stem cells: stimulation by parathyroid hormone

Abstract

With aging, there is a decline in bone mass and in osteoblast differentiation of human mesenchymal stem cells (hMSCs) in vitro. Osteoblastogenesis can be stimulated with 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] and, in some hMSCs, by the precursor 25-hydroxyvitamin D₃ (25OHD₃). CYP27B1/1α-hydroxylase activates 25OHD₃ and, to a variable degree, hMSCs express CYP27B1. In this study, we tested the hypotheses (i) that age affects responsiveness to 25OHD₃ and expression/activity of CYP27B1 in hMSCs and (ii) that parathyroid hormone (PTH) upregulates CYP27B1 in hMSCs, as it does in renal cells. There were age-related declines in osteoblastogenesis (n = 8, P = 0.0286) and in CYP27B1 gene expression (n = 27, r = −0.498; P = 0.008) in hMSCs. Unlike hMSCs from young subjects (≤50 years), hMSCs from older subjects (≥55 years) were resistant to 25OHD₃ stimulation of osteoblastogenesis. PTH1-34 (100 nm) provided hMSCs with responsiveness to 25OHD₃ (P = 0.0313, Wilcoxon matched pairs test) and with two episodes of increased 1,25(OH)₂D₃ synthesis, of cAMP response element binding protein (CREB) activation, and of CYP27B1 upregulation. Both increases in CYP27B1 expression by PTH were obliterated by CREB-siRNA or KG-501 (which specifically inhibits the downstream binding of activated CREB). Only the second period of CREB signaling was diminished by AG1024, an inhibitor of insulin-like growth factor-I receptor kinase. Thus, PTH stimulated hMSCs from elders with responsiveness to 25OHD₃ by upregulating expression/activity of CYP27B1 and did so through CREB and IGF-I pathways.